Process of manufacturing cellulose acetate



May 20 1924- P. c. SEEL PROCESS OF MANUFACTURING CELLULOSE ACETATE Filed Aug. 18 1923 hatente d May 2%, ldgd.

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FCESS OE MAHUFAGTURING GULOSE ACETATE.

Application filed August 18, 1923. Serial No. 658,109.

To all whom it may concern:

Be it known that 1, PAUL C. Sun, a citizen of the United States of erica, residcarried on until a chloroform-soluble cellulose acetate is produced. Then a hydrolyzing mixture containing a relatively small ing at Rochester, in the county of Monroe/ amount of water is introduced until the reaction converts the cellulose acetate into the and State of New York, have invented certain new and useful Improvements in Proc esses of Manufacturing Cellulose Acetate, of which the following is a full, clear, and exact specification.

This invention relates to processes of manufacturing cellulose acetate. One object of the invention is to lessen the cost of such manufacture. Another object of the invention is to provide a simple, rapid, and inexpensive process for recovering acetic values, such as acetic acid and aceticanhydride from the cellulose acetate reaction mixture. Still another object of the invention is to provide a process for recovering acetic values in a comparatively pure state without expensive chemical operations. A further object of'the invention is to provide a process in which a gaseous vehicle, such as air, is so used that it will take up vapors of the acetic values quickly and efiiciently. Another object of the invention is to provide a process in which the reaction. mixture is brought to and maintained in such a condition that it provides greatly increased surface for the evaporationv of volatile acetic values. Another object of the invention is to obtain the cellulose acetate, freed from the bulk of acetic values, in a form having a large aggregate surface which facilitates liquld treatment by washes, reaction baths, and solvents. Other ob jects will hereinafter appear.

In the'drawing,

Fig. 1 is a diagrammatic side elevation, partly in vertical section, showing one form of apparatus in which my process may be carried out, the relative sizes of the parts being exaggerated for the sake of clearness;

Fig. 2 is a horizontal sectional View of the mixing unit taken on the line 11-11 of Fig. 1.

Cellulose acetate is produced by the action able acetylating agents on cellulose in the p nee of catalysts. The reaction mixtu e in .y', for-example, initially comprise cellulose, acetic anhydride, acetic acid and sulfuric acid, and the products of the reaction as latter proceeds. An example of this general type is given in United States Reissue ?atent No. 12,637, Milesa Apr. 23,

F907. The acetylating reaction is at first acetone-soluble form. Before the hydrolyzing mixture acts, the excess or unused acetic anhydride is converted into acetic acid by the addition of the proper amount of water. Suficient Water can be introduced. in the hydrolyzing mixture to kill the acetic anhydride and cooperate in the conversion of the cellulose acetate.

If the reaction is terminated when the cellulose acetate is in the chloroform-soluble stage, a considerable amount of acetic values remain, such as acetic anhydride and acetic acid (and in some cases acetyl chloride). If the reaction be carried to the point where acetone-soluble cellulose acetate is produced, the acetic values will be in the form of acetic acid. Because of the relatively high value of these acetic values, they have a very important bearing upon the cost of the cellulose acetate which is produced. Their recovery substantially in condition for further acetylation, when effected inexpensive ly, greatly lowers the total cost of the mambfacturingoperations and thereby cheapens the cost of the product. a

The reaction mixture has heretofore been washed with, a considerable excess of water to free it from the acetic values. The recovery of these values from the comparatively dilute solutions which are produced can be carried out only at considerable expense. Water evaporating steps and chemlcal reaction steps have proven to be complicated and undesirably expensive.

I have found that the recovery of the acetic values can be simply and inexpensively carried out by separating at least the major portions of the acetic values from the reaction mixture by means of a gaseous vehicle, such as air. Preferably I pass the vehicle through the reaction mixture to take up vapors of'the acetic values and then re cover the values from the laden vehicle by condensation, absorption, or the like. I have found it preferable to pass the gas through the reaction mixture in a subdivided form, such as by forcing air bubbles through it, so that a lar e amount of surface is pre sented throug which vapors bf the acetic values may enter the gas. The reaction mixture is, broadly speaking, liquid, by which tit I mean that it is -2til flation enables the use of the air current, facilitating powdery nature.

flowable to a certain extent, even when it is sometimes thickened to a pasty condition.

- T have likewise found that the recovery of the acetic repeatedly circulating the gaseous vehicle, such as air, through the reaction mixture and the zone or station where the acetic values are removed from it. This recircua stronger con centration of the vapors of acetic values in condensation, and prevents an unremoved fraction of these values being wast d in the manner that would take place if the air were discharged into the atmosphere to carry away the unextracted vapors. I

l have also discovered that when the gaseous'vehicle is agitated through the reaction mixture for a suliicient time the latter changes from a liquid or viscous form to a mass of separate particles of a somewhat The aggregate surface of there'particles is much greater than the surface of the original reaction mixture. l have found that advantage can be taken of this large surface in the treatment of additional amounts of reaction mixture. When these amounts are stirred into the powdery mass and a aseous vehicle is passed through, the ad itional amounts of reaction mixture are uickly converted to a subdivided or pow ery condition, because of the except for the piping increased rapid evaporation taking place from the enlarged surface.

My process may be carried out in many types of apparatus, the one shown in the drawing being merely illustrative of a useful form. The main receptacle in which the gaseous vehicle and reaction mixture are brought into-intimate contact is indicated at 1. This is preferably an airtight vessel, hereinafter described. It may conveniently take the form of a well known mixer in which the bottom is divided into two troughs 2, 3 above which are located mixing blades 4 rotated withshafts 5, driven by any suitable means (not shown). These blades may be of a form which merely turns the material about the shafts, but I prefer to use blades which give a longitudinal movement to the mixture also. See, for example, U. S. Patent No. 534,968, Pfieiderer, Feb. 26, 1895. The receptacle may be temperature controlled by steam coils or any other well known and customarv way.

Entering into the reaction mixture 6 is a perforated transverse pipe 7 This connects with a vertical pipe 8 which passes through an airtight connection in the top 9. Pipe 8 is in turn connected bypipe line 10 with an air compressor or blower 11. The latter draws its supply of air through pipe 12; from the roval or recovery unit 13, which values is greatly. facilitated by jackets or.

acetate is in turn connected by pipe 14 with the top 9 of receptacle 1. ln the top 9 of the receptacle lth'e're is also located a normally closed or sealed loading fixture or pipe 15.

ll find it useful to have for slightly warmingthe gaseous vehicle be.- fore it enters the main mixing receptacle 1. This is indicated diagrammatically in the drawing as a casingl'? surrounding a section of pipe 10, through which warm water or exhaust steam is passed through-pipes-19 controlled by valves 20. The removal .station 13, where vapors of acetic values (usually the vapors of acetic acid) are separated from the air, may take the form of any well known absorption or condensation tower. This is conventionally indicated in Fig. 1 as a cooling chamber 21 surrounding a coil 22, the cooling medium being passed in and out by means of pipes 23 controlled by valves 24:. The entrance of additional air when required may be conveniently effected by tus a reaction mixture, such as any one of those shown at the difi'erent stages in the Miles patent cited above, is charged into receptacle 1 through pipe 15 until it rises above perforated pipe 7 The blades 4 are set in operation and the compressor or blower 11 started to force air through pipes 10, 8, and 7 into the reaction mixture 6. he bubbles thus formed in the mixture are agitated or forced through the material, the blades 4: assisting in this action. During this period the bubbles of the gaseous vehicle take up as much vapor of the acetic values as they can hold at the prevailing temperature. I have found it convenient to operate with the receptacle 1 and its contents at 80 to 85 F., but, of course, the thermal factors of a particular apparatus can be readily understood by those skilled in where they are condensed and may be drawn,

off through valves 27 in enlarged pipe 28. The amount of vapor which is condensed and removed at station 13 depends primarily upon the difference in temperature between it and receptacle 1. The condensing temperature is kept as low as practical without solidifying the acetic values which are condensed in it. I have found 60 F. to be useful when there is a slight amount of water present, because it enables the acetic acid to be condensed in the liquid form without clogging the condenser. This temperature, however, is of course, subject to adjustment, as will be understood by those smiled in the art. There will, of course, be

some vaporof acetic valuesleft in the air a heating unit 16' manipulating valve 25 in pipe 26. In carrying out my process in this appara- I rising from 1 nceaeiie after it leaves the condenser and when it reenters the mixture 6, butthe amount is sufficiently below the saturation point to avoid interference. with the process. In fact, it assists the dividing of the mixture into small particles; and assists the rate of evaporationbecause it prevents too hard and impervious a skin forming on the pieces of the mixture. [The cooled vehicle is -drawn through pipe 12 by the compresser'for blower 11. If .a compresser is emplo ed, it often times warms theair up su ciently to permitit to function properly when it passes through pipe 10 to the receptacle -1. 15 this to be true in one form of apparatus where the compresse'r is operating at from 3 to 5 pounds pressure. When, however, the compresser does not adequately warm the vehicle, 20,it is preferable to reheat the air to the required temperature (say 80 or 90 F.).by means of heating unit 16.

As the removal oft'he acetic values from the reaction mixture 6 progresses, the latter-i .25 changes over from a viscous or pasty liquid,

tional amounts of reaction mixture are distributed over the surfaces. of the particles, which surfaces in the aggregate are relatively large compared to't isrepeatedly broug t into contact with the additional reaction mixture and quickly re-.-

moves vapors of acetic yalues from it. The

powdery mass is increased by repeating the.-

charging of additional reaction mixture and continuing the blowin The powdery mass may thus be gradua 1 built up until it approaches the top of receptac e 1 'may then be removed through any suitable door,

such as 29, in receptacle The addition of the reaction mixture during the building up maybe carried out mtermittently or continuously, but in any event the rate of charging in' the mixture and the rate of passin the airthrough the mass are so correlate that' the kept up substantially enough to secure the advantages due to its increased evaporating 00 surface.

While the acetic acid vapors may be absorbed by' bubblingthe vapor-laden air rthro'ugh a suitable i ing the acid from such liquid, nevertheless I greatly prefer to use the condensation I have found or when a blower is employed,

dose-acetate reaction I I at of the ori 'nal- 40 -11qu1d. In this wayl the circulating've icle of the powdery mass owdery condition will beuid and then distill-- method described "above, because it recovers the acetic values in a form suflipure for reuse 1n further acetylaciently tion.

The powdery mass, because of its very large surface relative to its weight, can be very rapidly treated by liquids in the further stepsof manufacture, such as-by water for washing, or baths for further hydrolysis,

,or by solvents.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent 'is:

'1.- In the-process of manufacturing cellulose acetate, the step of passing a gaseous vehicle through a cellulose acetate reaction mixture containing volatile acetic values to .carryiaway vapors of said values.

- 2. In'the process of manufacturing cellulose acetate, the step of forcing air through a cellulose acetate reaction mixture containing acetic acid to remove acetic'acid there-- from.

3. In the process of manufacturing cellulose acetate, the ste of-forcing a gaseous vehicle in'subdivide form through a cellumixture containing vola'tile acetic values to increase the area of contact between. the mixture and vehicle and carry away vapors of acetic values therefro 4 .4. In the process of manufacturing cellulose "acetate, the step of forcing a1r bubbles through .a cellulose acetate reaction mixture containing acetic acid to carry away va ore of said acid 7 5'. In t e process of manufacturing cellulose acetate, the steps of passing a gaseous vehiclethrough' a cellulose acetate reaction mixture containing volatile acetic values to carryaway vapors of said values,"and re moving aceticvalue's from-said vapor-laden vehicle. 4

--6.,In the process of manufacturing cellu lose acetateytheisteps of forcing air through a cellulose acetate reaction mixture containing acetic acid to carry away acetic acid and removing acetic acid from said air.

7; Inrthefprocess of manufacturing cellulose=acetate,'repeatedly circulating a gaseous vehicle .througha cellulose acetate re action mixture containing volatile acetic values to take up. vapors of said values and through a removal zone' for removing acetic values fromthe-gvehicle.

8. In the process of manufacturing cellulose acetate repeatedly circulatin air through a cellulose acetate reaction mlxt-ure containing acetic-acid to taken the latter and through a condensing zone or'separa't inglacetic acid from-saidair. 9. In the process of manufacturing cellulose acetate, repeatedly'gcirculating a gaseous vehicle through a-- cellulose acetate reac- 1 tion mixture containing volatile acetic valass to take up vapor of said values, through a coolin zone for removing vapor of said values rom said vehicle, and through a warming zone to restore the original temperature of said vehicle. I

10. In the process of manufacturing cellulose acetate, removing volatile acetic values from a liquid cellulose acetate reaction mixture containing the same by passing a gaseous vehicle 1nto contact with said mlxture to carry away vapor of said values until said mixture is changed to a mass of substantially separate particles.

11. In the process ofmanufacturing cellulose acetate, the steps of passing a gaseous vehicle with agitation into contact with a liquid cellulose acetate reaction mixture containing volatile acetic values to carry away vapors of said values until said mixture is changed to a mass of substantially separate particles, spreading among said particles an additional amount of such mixture and passing such gaseous vehicle through said mass to carry away vapors of acetic values from said additional amount, the mass of particles being thereby increased.

12. In the process of manufacturing cellulose acetate, the steps of forcing a gaseous vehicle with agitatlon into contact with a normally liquid cellulose acetate reaction mixture containing acetic acid to carryaway acetic acid until said mixture is changed to a mass of particles having a greater aggregate surface than the surface of the original mixture, spreading an additional amount of such mixture among the surfaces of said particles and passing such vehicle among the particles to carry away acetic acid from said additional amount, the rate of spreading and the rate of passing the vehicle being correlated to in theform of particles with large aggregate surface, thereby increasing the rate of removal of acetic acid and building up the mass of particles.

13. In the process of manufacturing cellulose acetate, the step of forcing a gaseous vehicle in subdivided form through a normally liquid cellulose acetatereaction mixture containing volatile acetic values until sufficient of said values are removed to change the mixture into a mass of substantially separate particles. i

14. In the process. of manufacturing cellulose acetate, agitating air bubbles through a liquid cellulose acetate reaction mixture containing acetic acidthereby ladening the air with acetic acid vapor, and removing the laden air until the mixture assumes a powdery consistency.

15. In the process of manufacturing cellulose acetate, the steps of vehicle in subdivided form through a cellulose acetate reaction mixture containing volatile vacetic values, thereby ladening the effectively maintain said mass.

agitating a gaseous mergers I vehicle with vapor of said acetic values, removing the laden vehicle until the mixture changes to a powdery mass, mixing into said mass more of such reaction mixture, and passing such vehicle through the mass to carry away further acetic values, the powdery mass being thereby increased.

16. In the process of manufacturing cellulose acetate, the bubbles through a liquid cellulose acetate reaction mixture containing acetic acid, to laden the air with acetic acid vapor, removing the laden air until the mixture changes to a mass of powdery consistency, mixing into said mass further amounts 0 such reaction mixture, passing air through said mass to remove vapors of acetic acid from said further amounts, the mixing in of said further amounts and the passing of the air being correlated to -maintain the powdery consistency of the mass. Y

17. In the process of manufacturing cellulose acetate, removing volatile acetic values passing a gaseous steps of. agitating air vehicle with agitation into contact with a liquid cellulose acetate reaction mixture contaimng volatile acetlc values to carry away vapors of said values until said mixture is changed to a mass of substantially separate particles, spreading among said particles an additional amount of such mixture and passing such gaseous vehicle through said mass to carry away vapors of acetic values from said additional amount, the mass of particles being thereby increased, and separating acetic values from said vehicle.

-19. In the process of manufacturing cellulose acetate, repeatedly circulating a gaseous vehicle through a liquid cellulose acetate reaction mixture containing volatile acetic values to take up vapors of said values; and through a removal zone for removing acetic values from the vehicle, the circulation being continued until the mixture changes toea mass of substantially separate part1cles.

20. In the process of manufacturing cellusaid additional reaction mixture, the mass of particles being thereby increased.

21. In the process of manufacturing cellulose racetate, repeatedly circulating air through a liquid cellulose acetate reaction mixture containing acetic acid to take up pow vapor of said acid and through a condensing surface.

zone in which acetic acid is separated from the air 3 said circulating being continued until said mixture becomes a powdery mass mixing further reaction mixture into said weenie mass, and circulating air through said mass PAUL C. SEEL. 

